The dean of the college of sciences want to know if engineering or physics majors do better in math. The dean collects the math scores for a are partial SPSS results:
Compute the test statistic:
The investigator is specifically interested to test whether the scores of engineering and physics majors are equal or not.
Denote µ1 as the population mean score of engineering majors and µ2 as the population mean score of physics majors.
Null hypothesis:
H0 : μ1 = μ2
That is, there is no significant difference between the mean score of engineering majors and physics majors.
Alternative hypothesis:
H1 : μ1 ≠ μ2
That is, there is a significant difference between the mean score of engineering majors and physics majors.
In order to test the hypothesis regarding the significant difference between the means of two independent samples, when the population standard deviations are unknown an independent sample t-test is appropriate.
Pooled sample variance:
The standard deviation in the scores of engineering majors is s1 = 7.5425,
The standard deviation in the scores of physics majors is s2 = 5.6921.
The pooled sample variance is obtained as 44.6447 from the calculation given below:
Thus, the pooled sample variance is 44.6447.
Standard error:
The standard error of the difference of means is obtained as 2.9881 from the calculation given below:
Thus, the standard error of the difference of means is 2.9881.
Test statistic:
The test statistic is obtained as -2.4096 from the calculation given below:
Thus, the test statistic is -2.4096.
Critical value:
The level of significance is α = 0.05.
The critical value is obtained as ±2.1009 from the calculation given below:
Since, the t-distribution is symmetric, the two critical values are –t(α/2) = -2.1009 and +t(α/2) = +2.1009.
Decision rule:
Denote t as test statistic value and t(α/2) as the critical value.
Decision rule based on critical approach:
If t ≤ –t(α/2) (or) t ≥ t(α/2), then reject the null hypothesis H0.
If –t(α/2) < t < t(α/2), then fail to reject the null hypothesis H0.
Conclusion based on critical value approach:
The test statistic value is -2.4096 and critical value is ±2.1009.
Here, t ≤ –t(α/2). That is, -2.4096 (=t) < 2.1009 (= -t(α/2)).
By the rejection rule, reject the null hypothesis H0.
Therefore, there is a significant difference between the mean scores of engineering majors and physics majors.
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